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.\"     @(#)diff.1	8.1 (Berkeley) 6/30/93
.\"
.Dd $Mdocdate: February 13 2014 $
.Dt DIFF 1
.Os
.Sh NAME
.Nm diff
.Nd differential file and directory comparator
.Sh SYNOPSIS
.Nm diff
.Op Fl abdilpTtw
.Oo
.Fl c | e | f |
.Fl n | q | u
.Oc
.Op Fl I Ar pattern
.Op Fl L Ar label
.Ar file1 file2
.Nm diff
.Op Fl abdilpTtw
.Op Fl I Ar pattern
.Op Fl L Ar label
.Fl C Ar number
.Ar file1 file2
.Nm diff
.Op Fl abdiltw
.Op Fl I Ar pattern
.Fl D Ar string
.Ar file1 file2
.Nm diff
.Op Fl abdilpTtw
.Op Fl I Ar pattern
.Op Fl L Ar label
.Fl U Ar number
.Ar file1 file2
.Nm diff
.Op Fl abdilNPprsTtw
.Oo
.Fl c | e | f |
.Fl n | q | u
.Oc
.Op Fl I Ar pattern
.Bk -words
.Op Fl L Ar label
.Op Fl S Ar name
.Op Fl X Ar file
.Op Fl x Ar pattern
.Ek
.Ar dir1 dir2
.Sh DESCRIPTION
The
.Nm
utility compares the contents of
.Ar file1
and
.Ar file2
and writes to the standard output the list of changes necessary to
convert one file into the other.
No output is produced if the files are identical.
.Pp
Output options (mutually exclusive):
.Bl -tag -width Ds
.It Fl C Ar number
Like
.Fl c
but produces a diff with
.Ar number
lines of context.
.It Fl c
Produces a diff with 3 lines of context.
With
.Fl c
the output format is modified slightly:
the output begins with identification of the files involved and
their creation dates and then each change is separated
by a line with fifteen
.Li * Ns 's .
The lines removed from
.Ar file1
are marked with
.Sq \&-\ \& ;
those added to
.Ar file2
are marked
.Sq \+\ \& .
Lines which are changed from one file to the other are marked in
both files with
.Sq !\ \& .
Changes which lie within 3 lines of each other are grouped together on
output.
.It Fl D Ar string
Creates a merged version of
.Ar file1
and
.Ar file2
on the standard output, with C preprocessor controls included so that
a compilation of the result without defining
.Ar string
is equivalent to compiling
.Ar file1 ,
while defining
.Ar string
will yield
.Ar file2 .
.It Fl e
Produces output in a form suitable as input for the editor utility,
.Xr ed 1 ,
which can then be used to convert file1 into file2.
.Pp
Extra commands are added to the output when comparing directories with
.Fl e ,
so that the result is a
.Xr sh 1
script for converting text files which are common to the two directories
from their state in
.Ar dir1
to their state in
.Ar dir2 .
.It Fl f
Identical output to that of the
.Fl e
flag, but in reverse order.
It cannot be digested by
.Xr ed 1 .
.It Fl n
Produces a script similar to that of
.Fl e ,
but in the opposite order and with a count of changed lines on each
insert or delete command.
This is the form used by
.Xr rcsdiff 1 .
.It Fl q
Just print a line when the files differ.
Does not output a list of changes.
.It Fl U Ar number
Like
.Fl u
but produces a diff with
.Ar number
lines of context.
.It Fl u
Produces a
.Em unified
diff with 3 lines of context.
A unified diff is similar to the context diff produced by the
.Fl c
option.
However, unlike with
.Fl c ,
all lines to be changed (added and/or removed) are present in
a single section.
.El
.Pp
Comparison options:
.Bl -tag -width Ds
.It Fl a
Treat all files as
.Tn ASCII
text.
Normally
.Nm
will simply print
.Dq Binary files ... differ
if files contain binary characters.
Use of this option forces
.Nm
to produce a diff.
.It Fl b
Causes trailing blanks (spaces and tabs) to be ignored, and other
strings of blanks to compare equal.
.It Fl d
Try very hard to produce a diff as small as possible.
This may consume a lot of processing power and memory when processing
large files with many changes.
.It Fl I Ar pattern
Ignores changes, insertions, and deletions whose lines match the
extended regular expression
.Ar pattern .
Multiple
.Fl I
patterns may be specified.
All lines in the change must match some pattern for the change to be
ignored.
See
.Xr re_format 7
for more information on regular expression patterns.
.It Fl i
Ignores the case of letters.
E.g.,
.Dq A
will compare equal to
.Dq a .
.It Fl L Ar label
Print
.Ar label
instead of the first (and second, if this option is specified twice)
file name and time in the context or unified diff header.
.It Fl l
Long output format; each text file
.Nm diff Ns \'d
is piped through
.Xr pr 1
to paginate it;
other differences are remembered and summarized
after all text file differences are reported.
.It Fl p
With unified and context diffs, show with each change
the first 40 characters of the last line before the context beginning
with a letter, an underscore or a dollar sign.
For C source code following standard layout conventions, this will
show the prototype of the function the change applies to.
.It Fl T
Print a tab rather than a space before the rest of the line for the
normal, context or unified output formats.
This makes the alignment of tabs in the line consistent.
.It Fl t
Will expand tabs in output lines.
Normal or
.Fl c
output adds character(s) to the front of each line which may screw up
the indentation of the original source lines and make the output listing
difficult to interpret.
This option will preserve the original source's indentation.
.It Fl w
Is similar to
.Fl b
but causes whitespace (blanks and tabs) to be totally ignored.
E.g.,
.Dq if (\ \&a == b \&)
will compare equal to
.Dq if(a==b) .
.El
.Pp
Directory comparison options:
.Bl -tag -width Ds
.It Fl N
If a file is found in only one directory, act as if it was found in the
other directory too but was of zero size.
.It Fl P
If a file is found only in
.Ar dir2 ,
act as if it was found in
.Ar dir1
too but was of zero size.
.It Fl r
Causes application of
.Nm
recursively to common subdirectories encountered.
.It Fl S Ar name
Re-starts a directory
.Nm
in the middle, beginning with file
.Ar name .
.It Fl s
Causes
.Nm
to report files which are the same, which are otherwise not mentioned.
.It Fl X Ar file
Exclude files and subdirectories from comparison whose basenames match
lines in
.Ar file .
Multiple
.Fl X
options may be specified.
.It Fl x Ar pattern
Exclude files and subdirectories from comparison whose basenames match
.Ar pattern .
Patterns are matched using shell-style globbing via
.Xr fnmatch 3 .
Multiple
.Fl x
options may be specified.
.El
.Pp
If both arguments are directories,
.Nm
sorts the contents of the directories by name, and then runs the
regular file
.Nm
algorithm, producing a change list,
on text files which are different.
Binary files which differ,
common subdirectories, and files which appear in only one directory
are described as such.
In directory mode only regular files and directories are compared.
If a non-regular file such as a device special file or
.Tn FIFO
is encountered, a diagnostic message is printed.
.Pp
If only one of
.Ar file1
and
.Ar file2
is a directory,
.Nm
is applied to the non-directory file and the file contained in
the directory file with a filename that is the same as the
last component of the non-directory file.
.Pp
If either
.Ar file1
or
.Ar file2
is
.Sq - ,
the standard input is
used in its place.
.Ss Output Style
The default (without
.Fl e ,
.Fl c ,
or
.Fl n
.\" -C
options)
output contains lines of these forms, where
.Va XX , YY , ZZ , QQ
are line numbers respective of file order.
.Pp
.Bl -tag -width "XX,YYcZZ,QQ" -compact
.It Li XX Ns Ic a Ns Li YY
At (the end of) line
.Va XX
of
.Ar file1 ,
append the contents
of line
.Va YY
of
.Ar file2
to make them equal.
.It Li XX Ns Ic a Ns Li YY,ZZ
Same as above, but append the range of lines,
.Va YY
through
.Va ZZ
of
.Ar file2
to line
.Va XX
of file1.
.It Li XX Ns Ic d Ns Li YY
At line
.Va XX
delete
the line.
The value
.Va YY
tells to which line the change would bring
.Ar file1
in line with
.Ar file1 .
.It Li XX,YY Ns Ic d Ns Li ZZ
Delete the range of lines
.Va XX
through
.Va YY
in
.Ar file1 .
.It Li XX Ns Ic c Ns Li YY
Change the line
.Va XX
in
.Ar file1
to the line
.Va YY
in
.Ar file2 .
.It Li XX,YY Ns Ic c Ns Li ZZ
Replace the range of specified lines with the line
.Va ZZ .
.It Li XX,YY Ns Ic c Ns Li ZZ,QQ
Replace the range
.Va XX , Ns Va YY
from
.Ar file1
with the range
.Va ZZ , Ns Va QQ
from
.Ar file2 .
.El
.Pp
These lines resemble
.Xr ed 1
subcommands to convert
.Ar file1
into
.Ar file2 .
The line numbers before the action letters pertain to
.Ar file1 ;
those after pertain to
.Ar file2 .
Thus, by exchanging
.Ic a
for
.Ic d
and reading the line in reverse order, one can also
determine how to convert
.Ar file2
into
.Ar file1 .
As in
.Xr ed 1 ,
identical
pairs (where num1 = num2) are abbreviated as a single
number.
.Sh ENVIRONMENT
.Bl -tag -width TMPDIR
.It Ev TMPDIR
If the environment variable
.Ev TMPDIR
exists,
.Nm
will use the directory specified by
.Ev TMPDIR
as the temporary directory.
.El
.Sh FILES
.Bl -tag -width /tmp/diff.XXXXXXXX -compact
.It Pa /tmp/diff. Ns Ar XXXXXXXX
Temporary file used when comparing a device or the standard input.
Note that the temporary file is unlinked as soon as it is created
so it will not show up in a directory listing.
.El
.Sh EXIT STATUS
The
.Nm
utility exits with one of the following values:
.Pp
.Bl -tag -width Ds -offset indent -compact
.It 0
No differences were found.
.It 1
Differences were found.
.It >1
An error occurred.
.El
.Sh SEE ALSO
.Xr cmp 1 ,
.Xr comm 1 ,
.Xr diff3 1 ,
.Xr ed 1 ,
.Xr patch 1 ,
.Xr sdiff 1
.Rs
.%A James W. Hunt
.%A M. Douglas McIlroy
.%T "An Algorithm for Differential File Comparison"
.%J Computing Science Technical Report
.%Q Bell Laboratories 41
.%D June 1976
.Re
.Sh STANDARDS
The
.Nm
utility is compliant with the
.St -p1003.1-2008
specification.
.Pp
The flags
.Op Fl aDdIiLlNnPpqSsTtwXx ,
as well as the
.Ev TMPDIR
environment variable,
are extensions to that specification.
.Sh HISTORY
A
.Nm
command appeared in
.At v6 .
